preseed help ?

okay so me an my boyfriend had sex like a week after my period and somewhat 2 weeks before i still have a little while before i start but i already pee so much and have veiny boobs and just sooooo tired all the little hearts are days we had sex if im not pregnant how do u use preseed and does it work ? i have kinda irregular periods i still have them every month just a couple days late sometimes or early how did yall get pregnant snd is anyone dealing with the same issue as me ?